Residual fuels



RESIDUAL FUELS Filed Jan. 29, 1958K, Ser. No. 711,829

6 Claims. (Cl. Gil-35.6)

This invention relates to vanadium-containing petroleum fuels. Moreparticularly, it is concerned with rendering non-corrosive thoseresidual fuels which contain such an amount of vanadium as normally toyield a corrosive vanadium-containing ash upon combustion.

This :application is a continuation-impart of our copending applicationSerial No. 701,845, tiled December 10, v1957, and assigned to the sameassigneeas the instant application and now abandoned. Y

It has been observed that when a residual type fuel oil ,containingsubstantial amounts Aof vanadium is burned in furnaces, boilers and gasturbines, the ash resulting vfrom combustion of the fuel oil is highlycorrosive to .materialseof construction at elevated temperatures and.attacks such parts as boiler tubes, hangers, turbine blades, -and thelike. These .effects are particularly noticeable Vin gas turbines. Largegas turbines show promise of becoming an important type of industrialprime mover. Howeven economic considerations based on the efficiency ofthe gas turbine dictate the useof a fuel for this purpose which ischeaper Vthan a distillate diesel fuel; otherwise, .otheruforms-ofpowersuch as diesel engines be Vcome competitive with gas turbines. Y l

One of the main problems arising in the use of residual fuel oils inAgasturbines is the -corrosiveness induced by those residual fuelsYcontaining suficient;v amounts of vanadium to cause .,corrosion. lWhereno vanadium is presentor the amount of vanadium is small, no appreciablecorrosion is encountered. While many residual fuel oils asnormallyobtained inthe refinery contain so little fvanadium, or none, asto present noV corrosion problems,

such` non-corrosiveV fuel oils are not always available at' .the pointwhere the oil is to be used. In such instance, the cost oftransportation ofthe non-corrosive oil to the point of use is oftenprohibitive, and the residualoil `loses its competitive advantage. Thesefactors appear to militate against the extensive use` of Yresidual fueloils for gas turbines. VAside f1-om, corrosion, .theformation ofdeposits lupon the burning of `a, residual'fuel in a gas turbine-mayresult in unbalance of the turbine blades, `clogging of openings andreduced thermal eiciency of Ythe turbine. p l n ASubstantially identicalproblems are encounteredwhen using a-solid residual petroleum fuelontainingsubstantial amounts of vanadium. Thesefuels'are petroleum'residues obtained by-known methods YofV petroleum re- 'Vning suchas'deep vacuum Vreduction of asphaltic crudes toiobtain solid'residues,-visbreaking ofeliquid distillation bottoms followed'bydistillation toobtain solid` residues, coking--of liquidl distillation bottoms, and thelike. The solid residues'thus obtained are known variously as petro--leum pitchesorcokes vand -iind use as fuelsj' Sincen the vanadiumcontentofvthe original crude oilltends to concentrate in thezresidualfractions,` and since the' processing of atheresidual fractions to`solid residues results in fur,-

f 2 the vanadium corrosion problem tends to be intensified in using thesolid residues as fuel.

The vanadium-containing ash present in the -hot flue gas obtained fromthe burning of -a residual fuel containing substantial amounts ofvanadium compounds causes catastrophic corrosion of the turbine bladesand other metal parts in a gas turbine. The corrosive nature of the -ashappearsto be due to its vanadum oxide content. such as vanadium oxide(V205), which are formed on combustion of a residual fuel oil containingvanadium compounds, vigorously attack various metals, their alloys, andother materials at the elevated temperatures encountered in thecombustion gases, the rate of attack becoming progressively more severeas the temperature is increased. The vanadium-containing ash formsvdeposits on the parts affected and corrosively reacts with them. yIt isa hard, adherent material when cooled to ordinary temperatures.

It has already been proposed to employ in corrosive residual fuels smallamounts of certain metal compounds to mitigate the vanadium corrosion.Such compounds are of varying effectiveness and it has not always beenpossible to reduce vanadium induced corrosion to a minimum amount. f

It has now been discovered that residual petroleum fuels containingvanadium in an amount suflicient to yield a corrosivevanadium-containing ash upon combustioncan be rendered substantiallynon-corrosive by incorporating therein to form a uniform blend (1) anamount of a vanadium-free magnesium compound yielding about 1 atomweight of magnesium per atom Weight of vanadium in said fuel, and (2) anamount of a vanadium-free alkali metal compound yielding about 1 atomweight of alkali metal per atom Weight of vanadium in said fuel. In thefuel compositions of the invention the coaction of the two additivecompounds is such that the corrosion is reduced to. negligible amounts.

In the accompanying drawing, the single figure shows Van apparatus fortesting the corrosivity of residual fuel oil compositions.

The .type of residual fuel oils to which the invention is directed isexempliiied by No. 5, No. 6 and Bunker C fuel oils which contain asufficient amount of vanadium to` form a corrosive ash upon combustion.These are residual type fuel oils `obtained from petroleum by therconcentration of the vanadiumin .the solidresidues, Y.

methods known to the art. For example,'residual fuel oils are obtainedasliquid residua by the conventional distillation of total crudes, byatmospheric and vacuum reduction of total crudes, by the thermalcracking of topped crudes, by visbreaking heavy petroleum residua, yandother conventional treatments of heavy petroleum oils. Residua thusobtained are sometimes diluted with distillate fuel oil stocks, known ascutter stocks, and

Ythe invention also includes residual fuel oils so obtained,

provided that such oils contain sufficient vanadium normally to exhibitthe corrosion characteristics described herein. It should be understoodthat distillate fuel oils themselves contain either no vanadium or suchsmall amounts Vas to present no problem of corrosion. The total ashyfrom commercial residual fuel oils usually ranges from about 0.02 to0.2 percent by weight. The vanadium pentoxide (V205) content of suchashes ranges 'from zero to trace amounts up to about 5 percent by weightyfor low vanadium stocks, exhibiting no significant vanadium corrosionproblem, .to as much as percent by weight for some of the high vanadiumstocks, exhibiting severe corrosion.

The type of vanadiumcontaining solid residual fuels .to which theinvention is directed is exemplified by the .coke .obtainedin knownmanner bythe delayed thermal 2,949,008l Patented Aug. ..16, 196G-Certain inorganic compoundsl of vanadium,

coking or fiuidized coking of topped or reduced crude oils and by thepitches obtained in known manner by the deep vacuum reduction ofasphaltic crudes to obtain solid residues. These materials have ashcontents of the order of 0.18 percent by weight, more or less, andcontain corrosive amounts of vanadium when prepared from stockscontaining substantial amounts of vanadium. A typical pitch exhibitingcorrosive characteristics upon combustion had a softening point of 347F. and a vanadium content, as vanadium, kof 578 parts per million.

Any magnesium compound, organic or inorganic, which is free fromvanadium is used as the magnesium additive of the invention. Similarly,any organic or inorganic vanadium-free alkali metal compound isemployed. The alkali metals include sodium, `potassium, llithium, cesiumand rubidium; sodium and potassium `compounds are preferred. Suchinorganic alkali metal and magnesium compounds as the oxides,hydroxides, ac'etates, carbonates, silicates, oxalates, sulfates,nitrates, halides and the like are successfully employed. In thisconnection, the mixture of salts present in sea water, as disclosed inour copending application Serial No. 654,- 812, filed April 24, 1957,comprises a suitable alkali metal compound. Magnesium oxide and talc arepreferred inorganic magnesium compounds. The organic compounds ofmagnesium and the alkali metals include the oil-soluble andoil-dispersible salts of acidic organic compounds such as: (l) the fattyacids, eg., valerie, caproic, Z-ethylhexanoic, oleic, palmitic, stearic,linoleic, tall oil, and the like; (2) alkylaryl sulfonic acids, e.g.,oil-soluble petroleum sulfonic acids and dodecylbenzene sulfonic acid;(3) long chain alkylsulfuric acids, e.g., lauryl sulfuric acid; (4)petroleum naphthenic acids; (5) rosin and hydrogenated rosin; (6) alkylphenols, eg., iso-octyl phenol, t-butylphenol and the like; (7)alkylphenol suliides, e.g., bis(isooctyl phcnol)monosulde,bis(t-butylphenol)disulfide, and the like; (S) the acids obtained by theoxidation of petroleum waxes and other petroleum fractions; and (9)oil-soluble phenol-formaldehyde resins, e.g., the Amberols, such ast-butylphenolformaldehyde resin, and the like. Since the salts or soapsof such acidic organic compounds as the fatty acids, naphthenic acidsand rosins are relatively inexpensive and are easily prepared, these arepreferred materials for the organic additives.

When employing in residual fuels the inorganic additives of theinvention, it is desirable to use finely-divided materials. However, thedegree of subdivision is not critical. One requirement for using ainely-divided material is based upon the desirability of forming afairly stable dispersion or suspension of the additives when blendedwith a residual fuel oil. Furthermore, the more finely-divided materialsare more eflicient in forming uniform blendsand rendering non-corrosivethe relatively small amounts of vanadium in a residual fuel, whether thefuel be solid or liquid. The inorganic additives are therefore employedin a particle size range of less than 250 microns, preferably less than.50 microns. However, `where the inorganic additives are water-soluble,for eX- ample, in the case of magnesium sulfate, sodium carbonate, andthe like, it is not necessary to employ finelydivided materials since,if desired, the additives can be dissolved in Water to form a more orless concentrated solution and the Water solution emulsied in the fuel.

The organic additives of the invention are oil-soluble oroil-'dispersible and are therefore readily blended with residual fuelsto form uniform blends. Since on a weight basis in relation to the fuel,the Vamounts of the .additives are small, it is desirable to prepareconcentrated solutions or dispersions ofthe organic additives in anaphtha, kerosene or gas oil for convenience in compounding.

In the practice of the Yinvention with vanadium-con- :taining residualfuel oils, the mixture of additives is uniformly blended with'the oil inthe disclosed proportions.

This is accomplished by suspending the finely-divided dry additives inthe oil, emulsifying or dispersing a concentrated water solution of thewater-soluble inorganic additives in the oil, or dissolving ordispersing the organic additives in the oil. If desired, suitablesurface active agents, such as sorbitan monooleate and monolaurate andthe ethylene oxide condensation products thereof, glycerol monooleate,and the like, which promote the stability of the suspensions oremulsions can be employed.

In the practice of the invention with the solid residual fuels,incorporation of the additives of the invention is accomplished inseveral ways. The additives can be suspended, emulsiiied or dissolved inthe liquid vanadiumcontaining residual stocks or crude oil stocks fromwhich the solid residual fuels of the invention are derived, and themixture can then be subjected to the refining process which will producethe solid fuel. For example, in the production of a pitch by the deepvacuum reduction of an asphaltic crude oil, the additives or aVconcentrate thereofV are slurried with the oil in proportion to thevanadium content thereof, and the whole subjected to deep vacuumreduction to obtain a pitch containing the additives uniformly dispersedtherein. As still another alternative, particularly with a pitch whichVis withdrawn in molten form from the processing vessel, the additivescan be mixed with the molten pitch and the mixture allowed to solidifyafter which it is ground to the desired s1ze.

In the case of either liquid or solid residual fuels, the additives canbe separately ffed into the burner as concentrated solutions ordispersions. In such a case, it is preferred to meter the additives intothe fuel line just prior to the combustion zone. `In a gas turbine plantwhere the heat resisting metallic parts are exposed to hot combustiongases at temperatures of the order of 1200 F. and above, the additivescan be added separately from. the fuel either prior vto or Vduringcombustion itself, or even subsequent to combustion. However they mayspecifically be added, whether in admixture with or separately from thefuel, the additives are introduced into said plant upstream of the heatresisting meta-l parts to be protected from corrosion.

The magnesium compounds and the alkali metal compounds `are bothemployed in small, corrosion retarding amounts with respect to the fuel,and in such amounts with respect to each other as to minimize thecorrosiveness of the ash. For example, when the magnesium compound isemployed in the amount of 1 atom weight of magnesium per atom Weight ofvanadium, ordinarily yan amount of alkali metal compound yielding about1 -atom weight of alkali metal is suicient to reduce the corrosion tonegligible amounts.V

'Ihe following examples are further illustrative of `the invention.

EXAMPLE I With a residual fuel oil uniformly blend 0.015 percent vbyweight of magnesium oxide 4and 0.11 percent by weight of a solution ofsodium ypetroleum naphthenate in naphtha con-taining 7 percent by weightof sodium.Y The residual fuel `oil employed Ihas the followinginspection:

Sodium: ppm. of oil 2 The resulting composition has Aan atom weightratio of magnesium to vanadium of 1:1 and an atom weight ratio `ofsodium to vanadiumof v1:11.

A. EXAMPLE 1I Uniformly'blend withithe same residual fuel oil of ExampleI,Y0.15 percent by weight of a solution of the magnesium soap of talloil in naphtha containing 6 percent by weight of magnesium and 0.03percent by weight of potassium carbonate. The resulting fuel oilcomposition has an .atom weight ratio of magnesium to vanadium of y1:1and an atom weight ratio of potassium to vanadium of 1:1.

.. l. Y. EXAMPLE III To the same residual -fuel oil of Example I, addand uniformly blend `0.035 percent by Weight of the same talc used inthe composition of Example V and 0.02 percent by weight of sodiumcarbonate. The resulting fuel oil composition has an atom Weight ratioof magnesium to vanadium of 1:1 and an -atom weight ratio of sodium toVvanadium of 1:1;

In` order Vto test the effectiveness of the additives of this inventionunder conditions of burning residual fuels -in a gas turbine, theapparatus shown in the drawing is employed.: As shown therein, theresidual oil under test is introduced through line into a heating coil11 disposed in a tank of water 12 maintained at such temperature thatthe incoming fuel is preheated to a temperature of approximately 212 F.From the heating coil 11 the 'preheated oil is passed into an atomizinghead designated generally as 13. The preheated oil passes through :apassageway 14 into a nozzle 15 which consists of a #26 hypodermic needleof approximately 0.008 inch I.D. and 0.018 inch O.D. The tip of thenozzle is ground square and allowed to project slightly through anoriice 16 of approximately 0.020 inch diameter. The oriiice is suppliedwith 65 p.s.i.g. air for atomization of the fuel into the combustionchamber 21. The air is introduced through line l17, preheat coil 18 intank 12, and air passageways 19 and 20 in the -atomizing head 13. Theycombustion chamber 21 is made up of two concentric cylinders 22 and 23,respectively, welded to two end plates 24 and 25. Cylinder 22 has adiameter of 2 inches and cylinder Z3 -has a diameter of 3 inches; thelength of the cylinders between the end plates is 81/2 inches. End plate24 has a central opening 26 into which the atomizing head is inserted.End plate 25 has a one (l) inch opening "27 covered by a bale plate 28'mounted in front of -it to prevent direct blast of llame on the testspecimen 29. Opening 27 in end plate 25 discharges into a smallercylinder 30 having a diameter of 11/2 inches and a length of 6 inches.The specimen 29 is mounted near the downstream end of the cylinderapproximately 1% inches from the outlet thereof. Combustion air isintroduced iby means of air inlet 31 into the annulus between cylinders22 'and 23, thereby preheating the combustion air, and then throughthree pairs of 1%6 inch tangential air inlets 32 in the inner cylinder22. The iirst pair of air inlets is spaced 1A inch from end plate 24;the second pair 3%; inch from the rst; and the third 3 inches from thesecond. The additional heating required to bring the combustion productsto test temperature is supplied by an electric heating coil 33surrounding the outer cylinder '23. The entire combustion assembly issurrounded by suitable insulation 34. The test specimen 29 is a metaldisc one inch in diameter by 0.125 inch thick, with a hole in the centerby means of which the specimen is attached to a tube 35 containingthermocouples. The specimen and tube assembly are mounted on a suitablestand 36.

In conducting a test in the above-described apparatus, a weighed metalspecimen is exposed to the combustion products `of a residual fuel oil,the specimen being maintained at a selected test temperature of, forexample, 1350, 1450 or 1550 F. by the heat of the combustion products.The test is usually run for a period of 100 hours with the rate of fuelfeed being 1/2 pound per hour and the rate of atomizing air feed being 2pounds peflioui. "I'he Ycombustion air entering through air inletV31is"fed at 25 ypounds per hour. At the end of the test run thespecimen/is reweighed to determine the weight of deposits and is thendescaled with a conventional alkaline descaling salt in'molte/ncondition at 475 C. After descaling, the specimen isdipped in 6 Nhydrochloric acid containing a conventional pickling inhibitor, and isthen washed, dried and weighed. 'I'he loss in weight of theVspeciinenafter descaling is the corros-ion loss.

YTests are conducted in the yapparatus just described using a 25-20stainless steel asthe test specimen. The 'tests lare run for 100 hoursat a temperature of 1450 F. under theconditions described above. Testsare made with the fuel oil compositions of Examples I, V and V I, `withfuel oil compositions similar to those of theseexamples but containingonly one of the additives in varying proportions, and with theuncompounded residual fuelf'oil of Example I., The following table showslthe corrosion and deposits obtained.

.f Table l Y Atom Wt. Corrosion,

Fuel Y Ratm-Addi- Wt.I lossof Deposits, v tive MetalzV Specimen,Mg./Sq.ln.

Mg./Sq.ln.

,Y y m oundedFuel-'of Ex- Ugpl1t- 1, 580 1, 130 Fuei- Sodium Naphthenate. l 21g;

o Fuel Magnesium 0xide 1:1 940 228 D0 2:1 96 145 3:1 25 43 1:1 220 210 02:1 79 150 Compounded Fuel of Ex- M .Vzkl ample NV=1;1i i 0 57Compounded Fuel of Example III (ulfgggg 16 10o It will be seen from theabove'table that the magnesium additives and the lalkali metal additivesunexpectedly coact to minimize corrosion and deposits. This -issurprising when it is considered that, although the 1ndividual additivestend to reduce corrosion and deposits, they still permit corrosion. Thusthe use of a sodium additive alone in amounts yielding as much as 6 atomweights of sodium per atom weight of vanadium still permits corrosion,and' the magnesium additive used alone requires at least 3 atom weightsof magnesium per atom weight of vanadium before minimizing corrosion.With thecombination of additives disclosed, considerably smaller amountsof each additive can be employed and corrosion is nonetheless tonegligible amounts. Similar results to those shovwn for the specificadditives employed in the examples and in the above table are obtainedwhen using the other magnesium and -alkali metal compounds disclosed.

A typical analysis of the 25-20 stainless steel employed in the testingdescribed is shown in the following table in percent by weight:

scope of the appended claims.

We claim:

l. A fuel composition comprising a uniform blend of a major amount of aresidual petroleum fuel yielding a corrosive vanadium-containing ashupon combustion, an`

amount of a vanadium-free magnesium compound yielding about 1 atomWeight of magnesium per atom weight of vanadium in said fuel and anamount of a vanadiumfree alkali metal compound yielding about 1 atomWeight Iof alkali metal per atom weight of vanadium `in said fuel.'

2. The composition of claim l, wherein the fuel is a solid residualpetroleum fuel.

3. A fuel composition comprising a uniform blend of a major amount of aresidual fuel oil yielding a corrosive vanadium-containing ash uponcombustion, an amount of a vanadium-free magnesium compound yieldingabout l atom weight of magnesium per yatom Weight of vanadium in saidfuel oil and an amount of a vanadium-free sodium compound yielding about1 atom Weight of sodium per atom Weight of vanadium in said fuel oil. f

4. A fuel composition comprising a uniform blend of a major amount of aresidual fuel oil yielding a corrosive vanadium-containing ash uponcombustion, an amount of magnesium oxide yielding about 1 atom Weight ofmagnesium per atom weight of Vanadium in said fuel oil and an amount ofsodium naphthenate yielding about l atom weight of sodium per atomWeight of vanadium in said fuel oil.

5. A fuel composition comprising a uniform blend of a major amount of aresidual fuel oil yielding a corm l rosive vanadium-containing ash'-upon combustion, an

amount of talc yielding about l atom Weight of magnesium per atom Weight`of vanadium in said fuel oil and an amount of sodium carbonate yieldingabou 1 atom Weight' of sodium per atom Weight of vanadium in said fueloil.

6. ln a gas turbine plant in which arfuel oil containing vanadium isburned and which includes heat resisting metal-lic parts exposed to hotcombustion gases and liable to be corroded by the corrosiveVanadium-containing asn resulting from combustion of said oil, themethod of reducing said corrosion which comprises introducing into saidplant upstream of said parts a small amount .of a vanadium-free mixtureof ,a magnesium compound and an alkali metal `compound, the amount ofsaid magnesium compound being suilicient kto yield about 1 atom Weightof magnesium per atom weight of vanadium in said fuel oil and the amountof said alkali metal compound being -sufiioient to yield about l Vatomweight of alkali metal per atom'weight of vanadium .in said fuel oil.

References Cited in the file of this patent FOREIGN PATENTS 498,777Belgium Nov. 14, 1950 306,652 Switzerland Apr. 30, 1955 1,117,896 France7..-- Mar. 5, 1956 UNITED STATES PATENT OFFICE CERTIFICATE 0FvCORRECTION Patent No. 2,949,008 August l6 1960 Albert G Rocchini et al.

It is hereby certified that error appears in the-printed Specificationof' the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 5, lines 13 and l4, strike out "the same talc used in thecomposition of Example V1 and insert instead N- talc having a magnesiumcontent of 1867 per cent by weight =f=g column lines 14 and l5,l strikeout V and VI" and insert instead and lll Signed and sealed this llth dayof April 1961.,

(SEAL) Attest:

ERNEST W. sgwlDER ARTHUR W. CROCKER Attesting Officer ActingCommissioner of Patents

6. IN A GAS TURBINE PLANT IN WHICH A FUEL OIL CONTAINING VANADIUM ISBURNED AND WHICH INCLUDES HEAT RESISTING METALLIC PARTS EXPOSED TO HOTCOMBUSTION GASES AND LIABLE TO BE CORRODED BY THE CORROSIVEVANADIUM-CONTAINING ASH RESULTING FROM COMBUSTION OF SAID OIL, THEMETHOD OF REDUCING SAID CORROSION WHICH COMPRISES INTRODUCING INTO SAIDPLANT UPSTREAM OF SAID PARTS A SMALL AMOUNT OF A VANADIUM-FREE MIXTUREOF A MAGNESIUM COMPOUND AND AN ALKALI METAL COMPOUND, THE AMOUNT OF SAIDMAGNESIUM COMPOUND BEING SUFFICIENT TO YIELD ABOUT 1 ATOM WEIGHT OFMAGNESIUM PER ATOM WEIGHT OF VANADIUM IN SAID FUEL OIL AND THE AMOUNT OFSAID ALKALI METAL COMPOUND BEING SUFFICIENT TO YIELD ABOUT 1 ATOM WEIGHTOF ALKALI METAL PER ATOM WEIGHT OF VANADIUM IN SAID FUEL OIL.